1. Field of the Invention
The present invention relates to a method for controlling positioning of an actuator for reducing the rotational output of a motor via a wave gear device and providing output from a load shaft. More specifically, the present invention relates to a positioning control method of an actuator that is equipped with a wave gear device that makes it possible to use an exact linearization technique to inhibit any reduction in the accuracy with which positioning of the load shaft is controlled, as caused by the non-linear spring characteristics of the wave gear device.
2. Description of the Related Art
There is known in the art an actuator 1 in which a wave gear device 3 is employed as a drive for outputting a decelerated rotational output of a motor 2, as shown in FIG. 9. A controller 4 known in the art for controlling positioning of the actuator 1 of the above configuration performs a semi-closed loop control wherein the rotational position and rotational speed of a motor shaft 5 are detected by a sensor 6 attached to the motor shaft 5; and the rotation of the load shaft 7, which is the drive output shaft, is controlled based on the sensor readings. The characteristics of the wave gear device 3 greatly influence the positioning control characteristics of the load shaft 7 in such semi-closed loop control systems because driving of the motor 2 is not controlled by directly detecting rotational information relating to the load shaft 7.
Non-linear elastic deformation occurs between the input and output in the wave gear device when a load torque is applied, and is one factor preventing the load shaft from being controlled with a high degree of accuracy. The effects of the non-linear spring characteristic must be accounted for in order to achieve high-accuracy control of the load shaft.
Exact linearization of the input-output relationship is known as a control method for controlling non-linear elements. Exact linearization is a technique wherein a linearization feedback α(x) and an input conversion β(x) are performed as shown in FIG. 1, and linearization is accomplished by setting α(x) and β(x) so that the characteristics of the output y will be dny/dtn=v from the input v of the expansion system, which includes α(x) and β(x) (Non-Patent Reference 1).    [Non-Patent Reference 1] “Non-Linear System Theory”, Ishijima et al., Society of Instrument and Control Engineers, CORONA PUBLISHING CO., LTD., p. 141-168, 1993.